Fish diseases are not only detrimental to the physiological well being of fish, but also can adversely affect the physical appearance of otherwise viable fish. The prevention, control and treatment of diseases of fish and other aquatic organisms is important in all types of media and growth methods and is particularly important for aquacultures that are kept in artificial or confined environments, such as aquaria, ornamental ponds or aquaculture ponds, as well as various types of shipping containers or holding tanks used for ornamental or edible fish and other aquatic animals.
Aquaculture ponds and shipping conditions often introduce the organisms to stressful situations, e.g., crowding, low oxygen, high carbon dioxide, or contaminated water, causing the organisms to become more susceptible to disease pathogens, such as bacteria, fungi, viruses, and parasites. Such growing and shipping conditions may also expose fish to contaminated water, e.g., from natural waste products of fish or from decaying food or dead fish. Contaminated water is also an environment favoring the growth of pathogens that cause fish diseases.
The intensive use of toxic and environmentally non-friendly disinfectants and therapeutic agents in intensive aquaculture farming, both for edible and for ornamental aquaculture organisms, is a growing concern for human health and the environment. A good example is the infection with atypical strains of Aeromonas salmonicida which is known by such names as goldfish ulcer disease, carp erythrodermatitis, and ulcer disease of flounder, eel and salmon. The disease is one of the primary diseases in the aquaculture of edible fish like carp, and Salmon, and in the aquaculture of ornamental fish like goldfish and Koi.
The bacterium causes primary skin lesions and in most cases secondary infection by other bacteria, ectoparasites or fungi frequently, in which case the ulcers continue to develops. In many cases when massive secondary infection of the open ulcer takes place the original pathogen, namely the Aeromonas salmonicida, is not present any longer in the ulcer due to unfavorable physiological conditions of the tissue itself.
This primary and secondary infection mechanism poses a big difficulty for the growers. Preventive treatments are essential as fish may be carriers of the Aeromonas salmonicida, without exhibiting any clinical signs.
Poor body condition, poor water quality, overstocking, stress and other factors may predispose the fish to an outbreak of ulcerative disease. When an outbreak occurs Antibiotic therapy (such as florfenicol, oxytetracycline, potentiated sulphonamides) in medicated food or injections is used. Bath treatment is often ineffective and not economically worthwhile. All treatment options are costly and require high dosages of Antibiotics. Due to the misleading behavior of the pathogen and its ability to develop resistance to antibiotics, antibiotic therapy should be based on culture and sensitivity results.
When secondary infection frequently takes place a cocktail of drugs is required to cover the possible wide range of secondary pathogens.
The economical losses are huge and even if the fish survive the disease, in many cases noticeable scars are left on the fish which may cause them to be unmarketable, especially with ornamental fish. More and over, fish surviving disease outbreaks are recognized as carriers of the disease and may continue to infect the remaining population without themselves showing any outward signs of infection thus if an effective treatment is not applied to the whole flock, repeated outbreaks and cross contamination in the marketing supply chain (mainly ornamentals) may occur.
No single, nor an environmental friendly treatment which is effective for (i) preventive treatment, and (ii) specific treatment against Aeromonas salmonicida, and (iii) broad spectrum treatment against all possible secondary organisms which inhabit the open ulcer, bacteria, Fungi and ectoparasites, and (iv) supporting an effective recovery of the open ulcer and minimal or absence of a scar, it available these days in the market.
Another example is the common practice in fresh water fish against Saprolegnia. Saprolegnia is ubiquitous in freshwater ecosystems and is the main genus of water molds responsible for significant fungal infections of freshwater fish and eggs.
Saprolegnia has a large impact on salmonids, especially those in aquaculture. However, it can also infect a number of other teleosts as well. Channel catfish, pike, bass, elver and suckers, roach, orfe, carp, tench, lamprey, sturgeon, barramundi, tilapia, and mullet have been infected with Saprolegnia. It has also been associated with tropical fish, including the kissing gourami, guppy, swordfish and platyfish.
Fungal infections are difficult to prevent and treat. Therefore, proper use of chemicals may be necessary when a Saprolegnia is diagnosed. However, there are few chemicals approved for use in aquaculture in the United States.
Malachite green is considered the most effective chemical for controlling Saprolegnia. However, because of concerns about its potential activity as a carcinogen, teratogen, and/or mutagen, malachite green is banned in the United States and some other countries. Formalin is effective in treating Saprolegnia and is the only fungicide registered for use in aquaculture in the United States. However, there are concerns about its affect on both the environment and personnel who handle it.
Both agents, although their use is banned or severely restricted, continue to be used in many places by the industry in an uncontrolled manner due to the lack of effective substitutes. The massive alternative use of antibiotics is also a matter of concern to health and environmental authorities.
The use of anesthetics and antibiotics during transportation of organisms in the aquaculture supply chain is another matter of concern. Ornamental fish packaging systems are characterized by very high fish loading densities and high metabolic wastes in the transport water after shipment. The key limiting factor to increasing the fish loading density in a live—fish transport system is the deterioration of the quality of transport water due to accumulation of metabolic wastes. A variety of techniques have been used to manage this issue. They include starving of the fish before packaging, lowering the temperature of transport water, addition of anesthetics, ion exchange resin and drugs in the transport water. Commonly used compounds for anesthesia during transport include Tricaine (or benzocaine), quinaldine, Eugenol, carbon dioxide and clove oil. Many of the common anesthetic agents impose various limitations. For example, no compound belonging to the Tricaine group should be used within 21 days of harvesting fish for food. Although Quinaldine and Quinaldine Sulfate have been used successfully by fisheries workers, a number of severe adverse effects have been reported. The compounds are irritants to gills and to corneal tissue. In addition, the solvents used to dissolve quinaldine have been known to irritate fishery workers where ventilation of the work area is inadequate. Carbon dioxide gas is soluble in water and as such, has weakly acid properties. Typically the gas is bubbled in the water. It is difficult, however, to control the concentration of carbon dioxide by this method.
Bacterial growth is another major source of metabolic wastes. Bacteria not only increase the amount of metabolic waste but also weaken the fish or cause disease. Drugs such Neomycin sulphate, Methylene blue and Acriflavine, and others that are officially forbidden, are added to the transport water to control bacterial growth.
Many millions of ornamental aquaculture creatures are transported by air in long flights. This extremely stressful journey which in many cases causes a loss of up to 25% of the shipment upon arrival and during the first 7 days of recovery, is a source of major economic loss for the industry. As a result many exporters, although are officially not allowed to do so in the export to certain geographical areas like Europe, add antibiotics to the shipment medium.
No single environmentally friendly agent which combines wide spectrum therapeutic/disinfective (bacteria, fungus, parasites and viruses) properties and anesthetic properties is available in the market or has even been reported.
The transportation issue is not only of concern to the ornamental industry. Starting from treatments in the hatchery farms, through transportation of larva or juveniles to the growth locations (which are sometimes far from the hatchery sites), organism are exposed to intensive stress in the growth ponds in the fish farms as well as during final transportation of mature organisms. Thus, the use of antibiotics (and anesthetics during treatment or transportation), is unfortunately very common, even though it is forbidden in many parts of the world.
Aquaculture is the fastest growing food sector; it pertains to the cultivation of the natural produce of water (e.g., fish, shellfish, algae and other aquatic organisms). Subsets of aquaculture include for example Mariculture (aquaculture in the ocean); Algaculture (the production of kelp/seaweed and other algae); fish farming that is related to the raising of fish such as catfish, tilapia and milkfish in freshwater and brackish ponds or salmon or other fish in marine ponds; fresh and salt water shrimps and crab farming; and the growing of cultured pearls. In 2003, the total world production of fisheries product was 132.2 million tons of which aquaculture contributed 41.9 million tons or about 31% of the total world production. The growth rate of worldwide aquaculture has been very rapid, i.e., more than 10% per year for most species, while the contribution to the total from wild fisheries has been essentially flat for the last decade. Hence for example, in the U.S., approximately 90% of all shrimp consumed is farmed and imported.
Shrimp consumed in the United States are supplied from saltwater or fresh water farms. They all use intensive cultivation methods and the shrimp suffer from many diseases and viruses such as “white spot” and the Taurus virus. Confronting shrimp diseases is very difficult, though there are some processes that can be followed for disease prevention. Here too use of the problematic substances formaldehyde (20 ppm) and green malachite (0.01 ppm) is common. There are no effective antiviral agents for treatment for affected shrimp; viral infection can only be prevented following sanitary preventive methodologies.
Some of the natural products for treating aquaculture diseases disclose products which promote the recovery of injured or diseased fish and other aquatic animals, especially healing of damaged fish tissue; and U.S. Pat. No. 4,500,510 to Goldstein discloses a composition comprising an extract of the aloe vera Linne plant that is used to promote healing of damaged, fish tissue. It may be used with one or more agents for replacing the natural mucoprotein secretion which coats the skin and scales of fish. The composition may be added to either fresh water or salt water. Similarly, U.S. Pat. No. 6,537,591 to Yoshpa discloses a therapeutic method for treating diseased (fungal or bacterial diseases) or injured fish or other aquatic animals that includes administering to the fish or other aquatic animal an amount of Pimenta extract selected from the group consisting of Pimenta racemosa and Pimenta dioica sufficient to promote recovery of the diseased or injured fish or other aquatic animal. Yoshpa also discloses a prophylactic method for treating a disease-free fish or other aquatic animal, including adding Pimento extract selected from the group consisting of Pimenta racemosa and Pimenta dioica to the water containing or to contain the fish or other aquatic animal in an amount effective to promote resistance of the aquatic animal to bacterial and fungal disease.
U.S. Pat. No. 5,882,647 to Yoshpa discloses another method for promoting recovery of fish from bacterial and fungal diseases and from wounds and abrasions in diseased or injured aquatic animals that includes administering to the aquatic animals an amount of cajeput oil (“Vietnamese Cajeput Oil”) which promotes their recovery.
Fish disease therapies which promote inhibiting pathogen growth have an important advantage in reducing the use of potent drugs or chemicals with adverse side effects. Furthermore, treatment of individual diseased or injured fish usually entails exposure of healthy fish and all other beneficial organisms in the environment to the treatment composition as well. For this reason, reducing diseased, injured fish, other aquatic animals or plants also present in the water, are particularly preferred.
TTO is an essential oil characterized by a broad-spectrum antiseptic activity and is a very effective biocide against bacteria and fungi and as an insect repellant. TTO is commercially obtained by distillation of leaves of paperbark tree species Melaleuca alternifolia. The tree is indigenous to the moist, sub-tropical coast of northeastern New South Wales and southeast Queensland in Australia, and has evolved its own natural defenses against disease and its own natural repellants against insects.
It is known that the major antiseptic active component of the TTO is the Terpinen-4-ol family. Chemical analysis identified terpinen-4-ol (about 42%), α-terpineol (about 3%) and 1,8-cineole (about 2%, respectively, of tea tree oil) as the water soluble components of tea tree oil. The mode of action of TTO on its cellular target is to damage the pathogen's cell wall and membrane and subsequently to denature the cell constituents. The antiseptic actions of TTO are not impaired in the presence of blood, serum, pus, mucous discharge etc. An acquired immunity of microorganisms to many antibiotics and sulphonamide drugs does not occur with TTO.
Substantial microbiological testing of TTO has established in the literature typical inhibitory concentrations of the oil against a broad spectrum of microorganisms. Nevertheless, its sharp aromatic characteristics prevent its use “as is” in humans and animals and its phytotoxicity prevents its use in field crops. Many formulations have been suggested in the art, a few of which teach its use in emulsions. None of those formulations has demonstrated broad spectrum activity at an effective dosage on a verity of aquaculture pathogens, including bacteria, fungi, internal and external parasites and viruses, combined with applicability to aquaculture organisms. More so no mentioning was identified in the literature of the anesthetic properties of a given formulation using TTO, let along on the possibility to generate, and based on TTO the only active ingredient, a multipurpose product which is applied as therapeutic, disinfectant and/or anesthetic agent, and is highly useful for a long list of procedures in the aquaculture industry.
The fact that all this is generated with a safe and natural substance and formulation which is very friendly to the environment is only adding to the uniqueness of this invention.
While a few effective TTO-containing emulsion biocides have been published in the literature, none of these have demonstrated the properties mentioned nor have been designed to be used for aquaculture applications, organisms and pathogens. Thus for example, U.S. Pat. No. 5,610,189 to Whiteley discloses a disinfecting composition comprising stable aqueous solutions of (a) a blend of biocide active terpenes from TTO; (b) one or more biocide active surfactants; (c) one or more proton donor type biocides; and (d) a salt of mono, di- or trihydroxy aliphatic or aromatic acid. U.S. Pat. No. 6,197,305 to Friedman et al. discloses a composition for oral hygiene for treating a fungal infection, comprising: a mixture of herbal extracts; a mixture of essential oils such as TTO; and a pharmaceutical carrier; wherein said herbal extracts are each present in an amount of from about 1% to about 10% by weight, and each essential oil is present in an amount of from about 0.2% to about 2.0% by weight. Moreover, it has been shown that tea tree oil inhibits certain fungi (See for example Australian Journal of Experimental Agriculture 39:1, 86-81, 1999). The treatment was satisfactory as it killed the fungi to a large extent, mainly fungi that attack humans, while in plants it caused phytotoxicity to attacked plants.
Steverding et al. have studied the effect of Australian TTO (1-30 ppm) in Tween 80 (10%) emulsions on Gyrodactylus spp. infection of the three-spined stickleback Gasterosteus aculeatus (See Dis Aquat Organ. 2005 Aug. 9; 66(1):29-32). Gyrodactylids are the only parasitic worms that reproduce in situ on their host and lack a specific transmission stage, therefore they bridge the classical divide between microparasites (bacteria, viruses etc) and macroparasites (worms etc). The study has shows that “TTO has little effect on parasite burdens” and that “TTO does not completely remove all Gyrodactylus spp. worms within two days”; moreover, a significant contribution to the TTO efficacy was surprisingly attributed to the Tween 80 emulsifier.
Thus, natural nontoxic wide-spectrum treatments, especially those containing effective organic products, such as the tea tree oil applicable as therapeutic, preventive and as anesthetic agents are thus meeting the ever growing industrial need for safe treatment of aquaculture diseases.